U.S. Pat. Nos. 3,103,808 to P. Eichelberger and 3,737,767 to R. Slutsky disclose mechanism for testing the electrical lighting systems in trailers without requiring the presence of a tractor. I propose a mechanism that can be used to test both the trailer lighting system and the tractor electrical power supply system; the trailer test can be performed without the physical presence of a tractor, and the tractor test can be performed without the physical presence of a trailer.
U.S. Patent to I. Nolte disclose testing mechanisms that require the physical presence of both a tractor and a trailer to complete the test. I propose a system that has dual function test capability on a trailer or tractor without requirement for the physical presence of the other unit (trailer or tractor).